The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the electronics industry utilized various methods and structures to build voltage reference circuits. The voltage reference circuits generally were used to supply a stable reference voltage for use by other circuits such as a comparator circuit. One commonly used design technique to form the voltage reference circuits used a bandgap reference as a portion of the voltage reference circuit. One design parameter for the prior voltage reference circuits was to reduce variations in the reference voltage that resulted from variations in the value of the input voltage that was used to operate the voltage reference circuit. This is sometimes referred to as power supply rejection. The ratio of the change of the input voltage to the change on reference voltage was referred to as the power supply rejection ratio (PSSR). One example of a prior voltage reference circuit was disclosed in U.S. Pat. No. 6,972,549 that issued to Brass et al. on Dec. 6, 2005. However, such prior voltage reference circuits did not provide sufficient power supply rejection.
Accordingly, it is desirable to have a voltage reference circuit that has improved power supply rejection.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action.